This invention relates to an axial flow turbine machine for operation with an elastic fluid.
In particular, the invention concerns an axial flow turbine machine comprising two or more expansion or compression stages, i.e. having a rotor carrying drive blades arranged in two or more axially spaced circumferential rows and a stator carrying guide vanes arranged in one or more circumferential rows, wherein each one of the rows of guide vanes is disposed between two adjacent rows of drive blades.
In prior art, it is well known to produce multi-stage turbine machines by forming both the rotor and the stator in a number of sections to be assembled into a complete rotor and a complete stator. In bigger turbines, the guide vanes are formed as separate parts for mounting in rows in the stator, and the stator is divided into two longitudinal halves to be put together around the rotor, whereby the guide vane rows are introduced between the drive blade rows.
However, when producing small size turbines having a diameter of only 30-40 mm, it is not practically possible to use separate guide vanes in the stator. The radial size of the guide vanes in the high pressure stage may be as small as a fraction of a millimeter. Such small vanes have to be formed integral with the stator by machining or molding.
In British Patent No. 1 287 850, there is described a small size two-stage turbine in which the rotor is formed in one piece, including two rows of drive blades. Since the drive blades extend from an outer cylindrical surface, there is no problem machining them from the rotor body. The stator of this known turbine comprises one row of guide vanes which is located between the drive blade rows and which is formed by two semicircular ring elements provided with guide vanes on their outside. This means that the guide vanes are easily machinable from the outer surface of the ring elements.
On the other hand, this prior art guide vane arrangement means that the turbine is rather complicated as it comprises not only separate ring elements to form the stator but also separate sleeve elements for accomplishing an axial clamping of the ring elements in the housing. This also means that there is a nonfavourable air flow path through the turbine, because the guide vanes have a bigger radial extent than the drive blades for enabling the axial clamping of the stator ring elements. Thus, the air flow path is locally enlarged in the stator, which causes an undesirable turbulent air flow therethrough.
The primary object of the invention is to accomplish an axial flow turbine machine having two or more expansion or compression stages and which is inexpensive and easy both to manufacture and to assemble and which is suitable for production in small sizes.
A preferred embodiment of the invention is below described in detail with reference to the accompanying drawings.